The possibility of the development of hydrogen embrittlement processes increases in cathodic protection systems when cathodic overprotection occurs, and large amounts of hydrogen are produced. Additionally, the hydrogen embrittlement susceptibility of steel depends on solubility, diffusivity, and hydrogen trapping. This paper presents a numerical simulation of the reversible and irreversible hydrogen trapping effects on crack propagation in API 5CT P110 steel using a model based on a synthesis of fracture mechanics and continuum damage mechanics, in which the trapping term of the diffusion equation was replaced by the trapping terms of other more complete model. The simulation was performed with using a C(T) specimen loaded in the tensile opening mode, in the linear elastic regime, in plane strain state, under the action of a static mechanical loading and the effect of hydrogen. The simulations showed that the material degradation ahead of the crack tip increases with increases in hydrogen concentration at the crack tip due to the hydrogen trapping effect. Furthermore, the process of onset and crack growth in material with irreversible traps is slower than that in material with reversible traps. These results are consistent with macroscopic observations of the trapping effect, providing a better understanding of the hydrogen embrittlement in structural steels. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.